1. Field of the Invention
This invention relates in general to spindle motors for use in magnetic disc storage systems. More particularly, this invention relates to magnetic disc storage systems having spindle motors that use hydrodynamic bearings.
2. Description of Related Art
Data storage systems, such as disk drives, commonly make use of rotating storage disks. The storage disks are commonly magnetic disks but could also be optical. In a typical magnetic disk drive, a magnetic disk rotates at high speed and a transducing head uses air pressure to "fly" over the top surface of the disk. The transducing head records information on the disk surface by impressing a magnetic field on the disk. Information is read back using the head by detecting magnetization of the disk surface. The magnetic disk surface is divided in a plurality of concentric tracks. By moving the transducing head radially across the surface of the disk, the transducing head can read information from or write information to different tracks of the magnetic disk.
Spindle motors are commonly used to rotate magnetic disks at high speeds. Frequently, conventional spindle motors comprise small electric motors equipped with standard ball bearings. However, electric motors having ball bearings are known to experience problems such as runout or vibration that can prevent information from being accessed from disks rotated by the motors. This is especially true as advancements in data storage technology have increased magnetic disk storage densities. To overcome the problems associated with ball bearing electric motors, some disk drive systems now make use of electric motors having fluid hydrodynamic bearings. Bearings of this type are shown in U.S. Pat. No. 5,427,546 to Hensel, U.S. Pat. No. 5,516,212 to Titcomb and U.S. Pat. No. 5,707,154 to Ichiyama.
An exemplary hydrodynamic bearing typically includes a stationary shaft on which is mounted a rotary hub to which magnetic disks can be secured. There is no direct contact between the rotating hub and the shaft. Instead, a lubricating fluid forms a hydrodynamic bearing between the shaft and the rotary hub. Hydrodynamic pressure or pumping is frequently provided by a pattern of grooves, commonly in a herringbone configuration, defined either by the exterior surface of the shaft or the interior surface of the rotary hub. During rotation of the hub, the pattern of grooves provides sufficient hydrodynamic pressure to cause the lubricating fluid to act as a hydrostatic bearing between the shaft and the rotary hub. Frequently, capillary seals are used to retain the bearing fluid between the shaft and the rotary hub.
In certain prior art electric motors having hydrodynamic bearings, the shaft defines an axial bore that provides a reservoir for bearing fluid. In certain of such prior art motors, the axial bore has only one open end that is closed by a pin which is press fit within the bore. Because the bore has only one open end, the bore is difficult to clean. Consequently, it is possible for debris left within the bore to contaminate the bearing fluid. Additionally, when the pin is press fit within the bore, wear debris is generated by the pressing operation. This wear debris can contaminate the bearing fluid of the hydrodynamic bearing and lead to premature wear and failure of the electric motor.